I'm used to seeing people say "vim" where "vi" is meant (of which vim is but one (much enhanced) clone), so when you say you could switch out gcc for clang, or bash for zsh, could you not switch out vim for (e.g.) nvi[0]? If not, why not?
nvi provides a minimalist implementation of vi. If you feel comfortable with the vi keybindings in other editors, nvi will likely suffice. However, many vim users expect scriptability, programming language support, and numerous other features.
The analogous comparison would be between bash and posh/dash, or between gcc/clang and the Tiny C Compiler.
I haven't used nvi in several years (mostly because, unlike nvi, vim has become universally available on the systems I use), but it's not minimalist. nvi has a number of features that the original vi does not. Perl integration and infinite undo are two examples.
nvi definitely provides more features than the original vi, just not nearly as much as vim. And it doesn't have a comparable ecosystem of plugin/package developers around it, either.
Why would you want to switch out of vim ? It runs everywhere.
nvi is completely different, all the configurations and so on. Syntax files, plugins, you can't just move those over.
You're assuming a vim-centric point-of-view. Believe it or not, I don't use vim that much, and so I have no vim configuration/plugins to worry about. nvi happens to be where I spend the bulk of my time since I've cared what flavour of vi I'm using. So, I haven't "switched out of vim". I am genuinely interested in "what I'm missing" though. I occasionally trawl though youtube to look for videos, but I mostly haven't had my mind blown. I think I -would- like horizontal (or would you call it vertical?) screen splits where I have a left screen and a right screen (nvi provides splitting arranged above/below ea. other), and to fold sections of my work too, so I could (using my imagination here): ma (mark 'a), go to some other spot in the doc and: \(backslash)'a (fold the text from "here" to the 'a mark). That'd be immediately satisfying. Otherwise, I think nvi holds up really well for me.
I haven't used nvi in many years, but for me, vim is much more than just the vi key bindings. Absolutely core features for me include folding and the various syntax-related features (filetype identification, syntax highlighting, filetype-specific logic, etc.).
